1. Field of the Invention
This invention generally relates to a linear motion rolling contact guide unit generally comprised of a rail, a slider and a plurality of rolling members interposed between the rail and the slider, and, in particular, to improvements in a guide channel defined between the rail and the slider of such a linear motion rolling contact guide unit.
2. Description of the Prior Art
A linear motion rolling contact guide unit is well known and it generally includes a rail extending straight over a desired length, a slider slidably mounted on the rail and a plurality of rolling members, such as balls and rollers, interposed between the rail and the slider to provide a rolling contact therebetween. A typical prior art linear motion rolling contact guide unit using a plurality of balls as rolling members is schematically illustrated in FIGS. 3 through 7.
As shown in FIG. 3, the guide unit includes a rail 1 which extends straight over a desired length and which is generally rectangular or square in cross section and thus includes a top surface, a bottom surface and a pair of side surfaces. As best shown in FIG. 6, a pair of inner guide grooves 1a and 1b is formed on the opposite side surfaces of the rail 1. The guide unit also includes a slider 2 which has a generally inverted U-shaped cross section and thus which includes a horizontal section and a pair of vertical sections depending downward from the opposite sides of the horizontal section as best shown in FIG. 6. Accordingly, the slider 2 is slidably mounted on the rail 1 in a straddling manner. As also best shown in FIG. 6, an outer guide groove 2a, 2b is formed on the inner surface of each of the vertical sections of the slider 2 extending in parallel with and opposite to a corresponding inner guide groove 1a or 1b of the rail 1, so that a guide channel is defined by a pair of such inner and outer guide grooves 1a-2a or 1b-2b.
The slider 2 is provided with a pair of endless circulating paths, each of which includes a load path section, which corresponds to the guide channel 1a-2a or 1b-2b, a return path section 8 and a pair of curved connecting path sections 7 connecting the corresponding ends of the load and return path sections. And, each of the endless circulating paths is provided with a plurality of balls 3 as rolling members, and, thus, these balls 3 roll along the corresponding endless circulating path as a relative motion is created between the slider 2 and the rail 1. Those balls 3 which are located in the load path section or the guide channel 1a-2a or 1b-2b are partly received by the inner guide groove 1a or 1b of the rail 1 and at the same time partly received by the associated outer guide groove 2a or 2b of the slider 2 so that a rolling contact is provided between he rail 1 and the slider 2. Such a linear motion rolling contacting guide unit is advantageous since it can provide a linear relative motion between he rail 1 and the slider 2 over an indefinite discante theoretically without change in performance.
As best shown in FIG. 3, the slider 2 includes a pair of end blocks 4 one located at each of front and rear ends, and the end block 4 is formed with a par of curved connecting path sections 7 of the pair of endless circulating paths. As the slider 2 moves along the rail 1, the balls 2 roll into the return path section 8 from the load path section 1a-2a or 1b-2b through the associated curved connecting path sections 7 o vice versa, and, thus, the balls 3 may roll along the endless circulating the paths endlessly. An end seal 5 is sealingly attached to each of the end blocks 4 so as to prevent any foreign matter, such as debris and oil, from entering into the gap between the rail 1 and the slider 2. The slider 2 is also provided with a grease nipple 6 which allows to supply grease to a desired location i the slider 2.
FIGS. 4 and 5 schematically illustrate how a typical prior art guide unit having the above-descried structure is fixedly mounted on a desired object, such as a bed 9 of machining tools or the like. That is, as shown in FIG. 4, the rail 1 is brought into position by bringing one of its side surfaces 1c1 and 1c2 (1c2 in this example) in contact with a reference surface 9a of the bed 9, and, then, the rail 1 is bolted to the bed 9. As best shown in FIG. 5, rail 1 is typical formed with a plurality of mounting holes 1d spaced apart one another at a predetermined distance along the longitudinal axis of the rail 1, and bolts are threaded into threaded holes formed in the bed 9 through these mounting holes 1d.
FIG. 7 schematically illustrates the rolling contact condition at the guide channel or load path section when the guide unit is fixedly mounted on the bed 9 as shown in FIGS. 4 and 5. As best shown in FIG. 7, the inner guide groove 1a of the rail 1 is defined by a pair of upper and lower circular arc guide surfaces 1a1 and 1a2, and the outer guide groove 2a of the slider 2 is also defined by a pair of upper and lower circular arc guide surfaces 2al and 2a2. Under the assembled condition shown in FIG. 7, a hypothetical straight line A--A defined by connecting a contact point between the inner upper guide surface 1a2 and the ball 3 and another contact point between the outer lower guide surface 2al and the ball 3 forms an angle of 45.degree. with respect to a hypothetical horizontal line X--X extending through the center 0 of the ball 3 having a diameter of Dw. Likewise, a hypothetical straight line B--B defined by connecting a contact point between the inner lower guide surface 1a1 and the ball 3 and another contact point between the outer upper guide surface 2a2 and the ball 3 forms an angle of 45.degree. with respect to the hypothetical horizontal line X--X in the direction opposite to the line A--A. Thus, the four contact points between the ball 3 and the inner and outer guide surfaces 1a1, 1a2, 2al and 2a2 are arranged symmetrically with respect to the horizontal reference line X--X as well as the vertical reference line Y--Y.
However, the above-described structure may suffer from the following disadvantages. In the first place, if a slight mounting error is present between the rail 1 and the slider 2 or between adjacent rails 1 when two or more rails 1 are mounted in a line, a sliding resistance may be increased and may vary along the rail 1. If an external force is applied to the slider 2 vertically downward as indicated by the arrow Z with the presence of a slight mounting error between the rail 1 and the slider 2, the ball 3 would be shifted in position as indicated by the dotted line 3' so that the ball 3 may come into contact with a corner 2ae of the outer upper guide surface 2a2 to be damaged, which could also increase the sliding resistance.